The present invention is of importance for bright annealing of copper or copper alloys. To accomplish this purpose it is necessary to heat and cool the copper in an atmosphere that prevents an undesired chemical reaction on the surface of the copper. The protective atmosphere most commonly used is lean exothermic produced by the controlled combustion of a hydro-carbon fuel, normally natural gas, with air. To date there have been two basic approaches to the generation of this atmosphere, either externally in a separate chamber or internally in the furnace proper. There have been disadvantages to both approaches.
External atmosphere generation, the presently preferred approach, is easier to control and more reliable. However, the heat generated by combusting the hydrocarbon fuel has been to date wasted. And in today's energy crisis this is a definite disadvantage.
The internally produced atmosphere approach has the potential of utilizing all or at least much of the heat released in producing the atmosphere. But, to date there have been design problems.
First, it is extremely difficult to maintain the correct air to fuel ratio because the heat load of the furnace changes as the processing conditions change. The variation in operating pressures through the combustion system as the temperature control zones change the burner firing rates complicates the ratio control.
Second, as the through-put of copper product is reduced or stopped the heat requirement of the furnace falls below that released in producing sufficient atmosphere. Therefore, it has been necessary to incorporate a separate heat loss on/in the furnace to absorb the extra heat released by the combustion for producing atmosphere. This separate heat loss has normally been in the form of a constant energy drain on the furnace. Consequently, the energy savings have been minimized.